The present invention is generally directed to developer compositions and processes for the preparation thereof, and more specifically, the present invention is directed to developer compositions with high conductivities, for example, from about 10.sup.-12 (ohm-cm).sup.-1 to about 10.sup.-7 (ohm-cm).sup.-1. More specifically the present invention relates to carrier and developer preparative processes, comprising, for example, blending resin coated or uncoated carrier particles in a fluidized bed jet mill and continuously separating fine particles formed therein from the resulting blended carrier particles, to provide high conductivity developers which possess highly desirable developer, development, and image properties, for example, bulk density, mass flow, conductivity, and conductivity stability with respect to developer lifetime in a xerographic development environment, excellent triboelectric charge and charge stability with respect to developer lifetime in a xerographic development environment and as a function of ambient environment, particularly temperature and relative humidity.
A problem encountered with two component electrostatic developers is the phenomena known as "charge through", which is observed when fresh or replenishing toner is added to an developer contained in a developer housing after extended operation and limited toner throughput. Although not desired to be limited by theory, it is believed that charge through causes the fresh toner to acquire a very high level of charge of the same sign as the toner in the housing prior to addition of the fresh toner. At the same time, the toner that is already present in the developer, referred to as the incumbent toner, looses much of its existing charge, and in extreme cases some or even the majority of the incumbent toner acquires a charge opposite to that of its original charge. In a xerographic developer, this will cause the incumbent toner to be developed out in background areas of a xerographic print, which undesired background area development is an unacceptable and often considered a catastrophic image quality defect. Further, it is believed that charge through may be caused by low levels of fine particle contamination contained in the developer and which contamination is believed to arise from material which is stripped or abraded from the carrier particle surface, such as metallic asperities or resin coating. The contaminants are scavenged by toner particles already present in the developer and thereby adversely alters the charging properties of both incumbent toner and fresh toner.
The above mentioned problem and related problems are overcome in embodiments of the present invention.